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The Physician’s Perspective on What to Report

James Brink, MDYale University School of Medicine

Factors to Consider

• Dose Metrics:• Impact of body habitus

• Risk Estimates• Impact of age, life expectancy• Effective dose vs. organ

dose/risk

• Variations in Practice• Decision support

Automatic Tube Current Modulation

Courtesy of GE Heathcare, Inc.

Impact of Patient Weight on ACTM

• 91 pts for Chest, Abdomen, Pelvis CT w/ 64DCT– NI=11.5, 5mm, rot=1s, pitch=1, 120kV, mAmax=800 mA

• CTDIvol obtained from console + Impact Dose Calculator– organ doses computed for a 70kg patient

• Patient doses were calculated by correcting for pt. size

Dose vs. Weight

60kg 100kgCTDIvol 11 33 (3x)Liver (mGy) 16 34 (2x)

Effective Dose:Min – Max = 6 – 50 mSv

Israel, Cicchiello, Brink, Huda.AJR 2010; 195:1342–1346

40 60 80 100 120 140 160

Pt. Weight (kg)

CTDIvol (mGy)60

10

50

40

30

20

AAPM Working Group Report (#204)

Con

vers

ion

Fact

or32 cm 120 kVp

AAPM Report #204

Example: Abdominal CT in a Child

SSDE = 5.4 mGy x 2.50= 13.0 mGyCTDIvol = 5.40 mGy (32 cm phantom)

AP = 9.9cm Lat = 12.3cmSum = 22cm AAPM Report #204

Factors to Consider



dose/risk


Cancer Risk

• Fatal cancer risk to population 5% per Sv– Female neonate 30% per Sv– Male neonate 15% per Sv– Late middle-age 1% per Sv

• Presuming linear extrapolation to low dose:– Effective dose of 10 mSv Risk = 1 in 2000

Dixon, A.K. and P. Dendy, Spiral CT: how much does radiation dose matter?Lancet, 1998. 352: p. 1082-3.

Atomic Bomb Survivor Data

• Biggest longitudinal study to date– 35,000 survivors exposed to doses < 150 mSv

– Followed for cancer incidence over 55 years

– Direct, statistically significant evidence for risk in the dose range from 5 to 150 mSv

Pierce, DA and Preston, DL. Radiation-related cancer risks at low dosesamong atomic bomb survivors. Radiation Research, 2000. 154(2): p. 178-86.

Adapted from Pierce, D.A. and Preston, D.L.

Excess Relative Risk for Cancer Mortality (1950-1990) in A-bomb Survivors (all ages)

0

0.02

0.04

0.06

0.08

0.1

0 20 40 60 80 100 120 140

Dose (mSv)Dose Range for CT

1 in 2000

Cancer RiskX-rays, gamma rays, and neutrons--labeled as known carcinogens by NIEHS on January 2005

A CT examination with an effective dose of 10 mSv may be associated with an increase in the possibility of fatal cancer of approx. 1 chance in 2000. USFDA

Effect of LET on Mammalian Cells

Tubiana M, et al. The Linear No-Threshold Hypothesis is Inconsistent with Radiation Biologic and Experimental Data. Radiology 2009; 251:13-22

Based on animal and human data, “there is no evidence of a carcinogenic effect for acute irradiation at doses less than 100 mSv and for protracted irradiation at doses less than 500 mSv.”

Age vs. Risk of Ionizing Radiation

Health risks from exposure to low levels of ionizing radiation — BEIR VII.Washington, DC: National Academies Press, 2005.

Age Distribution of CT Scans

Mettler, et al. Health Physics 95(5):502-507; 2008

2003

Impact of Life Expectancy

Brenner DJ, Shuryak I, Einstein AJ. Radiology 2011;261:193-198

“For a 70-year-old patient with colon cancer, the estimated reduction in lifetime radiation-associated lung cancer risk is approximately 92% for stage IV disease, versus 8% for stage 0 or I”

Factors to Consider



dose/risk


Effective Dose = DLP x 0.017 mSv/mGy-cm= 57.8 mSv

(gated, but without tube current modulation)

Effective Dose

Estimate effective dose from DLP

Region mSv / mGy cmHead 0.0023Neck 0.0050Chest 0.017Abdomen 0.015Pelvis 0.019

Jessen KA. Applied Radiation and Isotopes, 1999; 165-172(This method is used in the ACR CT Accreditation Program)

Organ Dose and Risk Estimation

4-D CT – Parathyroid Adenoma

4-D CT vs. Sestamibi Scan

• 4-D CT: 1.25mm helical scan at 0, 30, 60, 90 sec– 120 kV, 128 mAs, CTDIvol=10.8 mGy, DLP=248 mGy cm

• SeS: 20 mCi of Tc-99m sestamibi• Dose Estimation:

– 4-D CT: ImPACT Dose Calculator– SeS: NUREG Method (US Nuclear Regulatory Commission)

• Cancer Risk Estimation:– Age and gender-dependent risk factors from BEIR VII

Parathyroid Imaging

• Effective Dose:–4-D CT: 10.4 mSv–SeS: 7.8 mSv

OrganDoses

Cancer RiskSeS 4-D CT

Factors to Consider



dose/risk


June 18, 2011

New York TimesJune 18, 2011

Imaging Pathways / Algorithms

• Practice of radiology is highly variable– Need to standardize our practices/processes among

institutions across the country

• Multidisciplinary diagnostic algorithms that go beyond appropriateness criteria

Diagnostic Algorithm for Suspected PE

http://www.imagingpathways.health.wa.gov.au

Australian Diagnostic Pathways

• Algorithms for Liver, Pancreas, Kidney, Adrenal• Next Steps:

– Seek buy-in from other professional societies– New effort for Adnexa, Vasculature, GB/ Biliary Tree, Spleen,

Lymph Nodes

JACR 2010;7:754-73

Radiology 2009; 251: 147-155

Radiology 2009; 251: 147-155

CT Utilization at MGH

# of CT scans ordered with CPOE/DS

PCP Practice Pattern VariationMRI L Spine for low back pain

Courtesy ofRamin Khorasani, MD, MPH

0%

20%

40%

60%

80%

100%

Pre-Intervention

PostIntervention

Appropriateness of L-Spine MRI for evaluation of low back pain by PCPs

Metric: Adherence toevidence-basedguidelines

>90%

42%

P=<0.001

Courtesy of Ramin Khorasani, MD, MPH

Complexity of Ordering Exams

Potential for error and risk reduction with decision support:

-- radiation exposure-- contrast misadministration

Items to ReportDecision support system

– Inform re trials, guidelines, level of evidence– Will reduce error in use of radiation, contrast media

Purpose in reporting– Benefit vs. risk (preferably organ vs. whole body)

Where to report, anticipated outcomes– In EMR, lower use; more within clinical trials– Need recommendations for cumulative dose

How long a period?– Indefinite to enable long-term follow-up– Need to consider body habitus, age, life expectancy

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